Medical Definition the Patellofemoral Joint

Where the Kneecap and the Thigh Bone Meet

knee anatomy
Credit: Image courtesy A.D.A..M.

The patellofemoral joint is where your patella (kneecap) and femur (thigh bone) meet at the front of your knee. The underside of your kneecap sits in a groove within your thigh bone called the patellofemoral groove. Within this groove, the kneecap mostly moves lengthwise, but it has some side-to-side movement and can tilt and rotate as well.

When you contract the quadriceps muscles of your thigh, they pull on the quadriceps tendon that attaches to your kneecap.

This makes your knee straighten. Two other thigh muscles keep your kneecap in the femoral groove during this motion -- the vastus medialis obliquus and the vastus lateralis, located on the inside and the outside of your thigh.

How You Use Your Patellofemoral Joints in Physical Activity

Some daily motions that "work" your patellofemoral joints include:

  • Walking uphill or downhill
  • Going up or down stairs
  • Kneeling, squatting, or getting up from a seated position

These are the types of everyday activities the patellofemoral joint was designed and evolved to perform. It works well, but, like the rest of your body, it undergoes wear and tear from almost constant use over the years. In addition, taking part in sports can lead to overuse and even abuse of the patellofemoral joint.

Patellofemoral Pain Syndrome

Misalignment or repeated contact of the joint surfaces may lead to patellofemoral pain syndrome, which is characterized by joint irritation and inflammation, knee pain, and limited range of motion in the knee.

The key symptom of patellofemoral pain syndrome is pain under and around your kneecap. 

Irritation of this joint is generally caused by the following factors:

  • Acute injury to the kneecap, such as a blow to the knee, falling on the knee, wrenching the knee with a sudden twisting motion, or getting tackled in football
  • Misalignment of the joint -- for example, when the kneecap no longer "tracks" properly within the patellofemoral groove
  • Overuse from excessive running, particularly if the knee muscles are weak (the reason why "runner's knee" is another name for this syndrome)
  • Chronic wear and tear of the knee joint from everyday activity and sports
  • Poor foot mechanics

Chondromalacia

Patellofemoral irritation may also lead to breakdown of cartilage (flexible connective tissue) on the underside of the kneecap (chondromalacia. In its most chronic form, this condition may require surgical repair. This is a common injury in runners, soccer players, skiers, and cyclists.

Symptoms of chondromalacia include a dull pain under or around the kneecap. This may be felt when going down or up stairs or getting out of a chair. Chondromalacia can be due to long-term wear and tear, muscle weakness, or knee-alignment problems, or it can develop after a fall.

Patellar Dislocation

Knee dislocations happen when the kneecap slips out of the patellofemoral groove.

This is very painful and can damage the joint cartilage. Causes of patellar dislocation include:

  • Having a shallow patellofemoral groove
  • Having a "high-riding" kneecap (more common in girls), a condition called patella alta, that makes it easier for the kneecap to slip out of the groove and dislocate -- for example, because of a strong contraction of the quadiceps or a blow or injury to the knee

More: Kneecap Dislocations

Sources:

"Patellofemoral pain syndrome patient handout." American Academy of Family Physicians (1999). 

Post WR. "Anterior knee pain: diagnosis and treatment." J Am Acad Orthop Surg. 2005;13(8): 534-543.

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